From Wikipedia:
Peter Paul Strzok II is a former United States Federal Bureau of Investigation (FBI) agent. Strzok was the Chief of the Counterespionage Section and led the FBI's investigation into Hillary Clinton's use of a personal email server.
Strzok rose to become the Deputy Assistant Director of the Counterintelligence Division, the second-highest position in that division. He also led the FBI's investigation into Russian interference in the 2016 United States elections.